Recently, as personal computers and televisions have been become lighter and slimmer, display devices have also been required to become lighter and slimmer, and flat displays such as liquid crystal displays (LCD) other than cathode ray tubes (CRT) have been increasingly researched according to the requirements.
The liquid crystal display (LCD) is a display device for acquiring a desired video signal by applying an electric field to a liquid crystal material having an anisotropic dielectric constant and injected between two substrates, controlling an intensity of the electric field, and controlling the light transmitted to the substrates from an external light source (a back light).
The liquid crystal display (LCD) is representative of the portable flat panel displays, and a thin film transistor liquid crystal display (TFT-LCD) using a thin film transistor (TFT) as a switch is mainly used.
The liquid crystal display (LCD) applies a voltage to the two electrodes to generate an electric field on a liquid crystal layer, controls the intensity of the electric field to control the transmittance of the light passing through the liquid crystal layer, and thereby acquires a desired image. The liquid crystal display (LCD) inverts the voltage polarity of a data signal for a common voltage (Vcom) for each frame, row, or pixel in order to prevent a degradation phenomenon that occurs when an electric field is applied in one direction to the liquid crystal layer for a long time.
In this instance, the voltage of the data signal is transmitted to the liquid crystal layer through a data driver including an amplifying circuit for amplifying the voltage of the data signal.
The amplifying circuit is disclosed in Korean Patent No. 10-2005-0030570, and the disclosed conventional amplifying circuit has an inverting input terminal coupled to a pair of input transistors having different two types and a non-inverting input terminal coupled to a pair of input transistors of two different types according to a rail-to-rail structure. The conventional amplifying circuit will now be described with reference to FIG. 1 and FIG. 2.
FIG. 1 shows a brief conventional amplifying circuit.
As shown in FIG. 1, the conventional amplifying circuit 1 generates an output voltage by using an amplifier 40 and output transistors 31 and 32 of different types, and transmits a generated output voltage to a pixel (the pixel is not directly shown and a capacitor of the pixel is shown as Cp in FIG. 1). Also, the same voltage as the output voltage transmitted to the pixel is input to the inverting input terminal (−) of the amplifying circuit. In this instance, when an input voltage is applied to the non-inverting input terminal (+) of the amplifying circuit, the voltage of the pixel capacitor (Cp) is charged or discharged according to the input voltage applied to the non-inverting input terminal (+) and the previous output voltage input to the inverting input terminal (−).
FIG. 2 shows a conventional amplifying circuit in detail.
As shown in FIG. 2, the conventional amplifying circuit 1 includes an input unit 10, a bias unit 20, and an output unit 30. In FIG. 2, transistors 11, 12, 17, 18, 19_2, 23, 24, and 32 are N-channel field effect transistors (i.e., N-channel metal oxide semiconductors), and transistors 13, 14, 15, 16, 19_1, 21, 22, and 31 are P-channel field effect transistors (i.e., P-channel metal oxide semiconductors).
The input unit 10 includes the transistors 11, 12, 13, 14, 15, 16, 17, 18, 19_1, and 19_2, and bias voltages BV1 and BV6 are applied to the transistors 19_1 and 19_2. In this instance, the amplifying circuit of the rail-to-rail structure has an inverting input terminal (−) coupled to gate electrodes of the transistors 11 and 13, and a non-inverting input terminal (+) coupled to gate electrodes of the transistors 12 and 14.
The bias unit 20 includes transistors 21, 22, 23, and 24 to which bias voltages BV2, BV3, BV4, and BV5 are applied.
The output unit 30 includes transistors 31 and 32 and capacitors 33 and 34. A gate electrode of the transistor 31 is coupled to a node A and a gate electrode of the transistor 32 is coupled to a node B to transmit the output voltage.
Accordingly, the conventional amplifying circuit has a problem of increasing the area occupied by the input transistor from among the entire area of the amplifying circuit because of adopting the rail-to-rail structure, and generates a problem of increasing power consumption because constant current sources for the input transistors of different types must be used.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.